[Serusers] succesive calls rejected (radius+mediaproxy)

Hallo, i'm using radius+mediaproxy and since I moved my sip proxy on a public ip I have the folowing problem. I log in regulary and make my firs call with no problem. But When I hung up, and after few minutes call again, my proxy wont authorise me. I get a message that I need to authorise with proxy. During that my FRERADIUS is recieving requests for authorisation. The second i get rejected i call again and it connects me. I tried lowering nat_ping intervals but no succes. my Invite snippet is a common one: sl_send_reply("100", "Trying"); if (!radius_proxy_authorize("")) { proxy_challenge("","0"); break; } else if (!check_from()) { sl_send_reply("403", "Use From=ID"); break; };